Adds msw@ to services/ui/OWNERS

BUG=none
TEST=none
TBR=msw@chromium.org

Change-Id: I7b5ef0675bdc920380fccd3c78d1860f01c7f34c
Reviewed-on: https://chromium-review.googlesource.com/1112626Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569831}

services/ui/OWNERS

 # COMPONENT: Internals>Services>WindowService
 
 ben@chromium.org
-erg@chromium.org
+msw@chromium.org
 sadrul@chromium.org
 sky@chromium.org